Understanding BS EN 771-3: Aggregate concrete masonry units

• DurabilityGenerally durability compliance criteria are to be found in BS 5628-3.• Water absorption by capillarityWater absorption is only applicable to facing units with no applied finish.The appropriate test method is BS EN 772-11, (Clay and aircrete unitsuse the same test method but using different procedures within themethod and these will lead to test results for the products, which cannotbe directly compared).• Moisture movementThis will now be declared to a new test method, which is a combination ofdrying shrinkage and wetting expansion.The appropriate test method is BS EN 772-14 (Aircrete is tested toBS EN 680 and this will lead to lower values which cannot be compareddirectly with results to BS EN 772-14).• Water vapour permeabilityTabulated values are likely to be declared in accordance BS EN 1745,BS 5250 & CIBSE Guide Book. If tested, values can be determined toBS EN ISO 12572.• Reaction to fire (spread of flame)If the manufacturer uses materials that result in a unit containing more than1% by mass or volume of organic material then he is responsible for thefollowing tests to be carried out:BS EN ISO 1182 Reaction to fire tests for building materials.Non- combustibility test.BS EN ISO 1716 Reaction to fire test for building materials – Determination ofthe heat of combustion.And the results need to be classified according to BS EN 13501-1.• Shear bond strengthA value of shear bond strength needs to be given and it is recommended thatthe tabulated value of 0.15 N/mm from Annex C of BS EN 998-2 is declared.(The tabulated value or a measured value is of no practical use as bondstrength in practice will be dependent on a number of factors outside thecontrol of the producer and a value could not be guaranteed as beinguniversally applicable, but only for a set of specific conditions, which wouldbe difficult to replicate on site).4